Typically the wireless communication system was developed for providing a voice service while guaranteeing user's activity. The wireless communication system is then expanding gradually its service region to a data service as well as the voice service and is now developed to the extent capable of offering a high-speed data service. The currently available wireless communication system, however, confronts a shortage of resources and users' demands for much higher-speed service, so that a more advanced wireless communication system is needed.
As one of next generation wireless communication systems developed to meet these needs, LTE (Long Term Evolution) was standardized in the 3GPP. LTE is technology for realizing high-speed packet based communication having the maximum transfer rate of about 100 Mbps. For this, some schemes are under discussion, for example, a scheme of reducing the number of nodes deployed on a communication channel by simplifying the architecture of a network, a scheme of maximally rendering a wireless protocol close to a wireless channel, and the like.
In order to increase the degree of freedom in the configuration of an operator's network, the LTE system supports interworking with an access network of non-3GPP, which is not standardized in the 3GPP, as well as E-UTRAN which uses the LTE transfer technology for a RAN (Radio Access Network) which interworks with a core network. Although various ways of interworking between a non-3GPP access network and an LTE core network can be used, an ePDG (Evolved Packet Data Gateway) is normally used for interworking between the non-3GPP access network and the LTE core network.